In order to suppress a sharp change in output shaft torque during a shift, that is, a shift shock, input torque to an automatic transmission is temporarily reduced. That is, an engine is controlled so that engine torque is reduced immediately before the end of an inertia phase during a downshift. If the input torque at a time point of synchronizing to a gear after the shift is great, then the change in the output shaft torque also becomes great. This disadvantageously increases the shift shock. Further, if torque on a frictional engagement apparatus that is engaged to perform the shift is small, the engagement timing thereof is disadvantageously delayed. Accordingly, in order to solve such problems, the engine torque is reduced immediately before the end of the inertia phase to reduce the shift shock.
Meanwhile, as shift manners of an automatic transmission, a simultaneous shift, a clutch-to-clutch shift and the like are known. The simultaneous shift of the former is a shift manner implemented with an automatic transmission having a main transmission portion for setting the reverse gear and three forward gears and a sub-transmission portion arranged in front of the main transmission portion for implementing two gears of high-speed gear and low-speed gear, wherein the main transmission portion and the sub-transmission portion are both switched so that a prescribed gear is implemented by the automatic transmission as a whole. The clutch-to-clutch shift of the latter is a shift manner wherein, for example, a clutch coupling an input shaft and a prescribed rotary member is disengaged, and another clutch is engaged to couple the input shaft and another rotary member. In these shift manners also, the shift shock can be reduced by reducing the input torque.
However, the torque acting on the frictional engagement apparatuses being switched is not always constant. Therefore, if the timing where the input torque is reduced is uniformly set to a certain timing immediately before the end of an inertia phase, more specifically, to a prescribed time point determined by a sensed rotational speed, problems such as follow may occur. That is, if a power-on downshift (a downshift in the driving state by the engine) is performed in a low-speed range, completion of engagement of the frictional engagement apparatus is delayed relative to completion of disengagement, due to great input torque to the automatic transmission and a small rotational change quantity by the shift. As a result, when a frictional engagement apparatus of the sub-transmission portion is engaged so that it is switched to the high-speed gear and the main transmission portion is downshifted so that the downshift is implemented as a whole, despite the reduction control for the input torque being performed, the sub-transmission portion upshifts after the downshift by the main transmission portion is completed. This may increase the shift shock. As to the clutch-to-clutch shift, both of the two clutches to be switched have their torque capacities reduced temporarily, and the engine rotational speed (the turbine rotational speed) may be revved up.
Japanese Patent Laying-Open No. 05-099323 discloses a shift control apparatus with which reduction control of input torque corresponding to a traveling state is performed to realize excellent shift characteristics. The shift control apparatus controls an automatic transmission in which a shift that causes a frictional engagement apparatus to be engaged during a shift occurs, the shift control apparatus including: power-on downshift sensing means for sensing a shift that causes a frictional engagement apparatus to be engaged during a downshift in a driving state; traveling state determining means for determining whether a traveling state is a traveling state in which input torque to the automatic transmission is great and in which a rotational change quantity of a prescribed rotary member associated with the downshift is small; torque down timing setting means for setting a timing of initiating control of reducing input torque when the traveling state determining means determines that it is the traveling state in which input torque to the automatic transmission is great and in which a rotational change quantity of a prescribed rotary member associated with the downshift is small to an earlier timing as compared to a timing of initiating control of reducing input torque when the traveling state determining means determines that it is not that traveling state; and torque reducing means for reducing the input torque to the timing being set.
According to this shift control apparatus for an automatic transmission, a shift that causes a frictional engagement apparatus to be engaged during a shift may occur. If such a shift is a downshift in a driving state, it is sensed by the power-on downshift sensing means. With the present traveling state, the traveling state determining means determines whether it is a traveling state in which input torque to the automatic transmission is great and in which a rotational change quantity of a prescribed rotary member associated with the downshift is small. When the power-on downshift sensing means senses the downshift and the traveling state determining means determines the traveling state, the torque down timing setting means sets the timing of reducing input torque to the automatic transmission, wherein the timing of initiating the torque reduction control when the traveling state in which input torque is great and in which a rotational change quantity of a rotary member is small is determined is set to be earlier than the timing of initiating the torque reduction control when the traveling state is determined not to be such a traveling state. Then, in accordance with the timing being set, the torque reducing means reduces the input torque. Therefore, since the input torque is reduced at the earlier timing during the shift in the traveling state in which the input torque is great and the rotational change quantity of a rotary member is small, a delay in the engagement of the frictional engagement apparatus is prevented, and as a result, the shift characteristics are improved.
However, in the aforementioned publication, the timing of recovery from the torque down control (the engine torque recovery) is set to the timing at which the turbine rotational speed (to be exact, the output rotational speed of the second transmission portion in the aforementioned publication) approximates the synchronous rotational speed of the gear after the power-on downshift (the value up to the synchronous rotational speed becomes at most β). If recovery from the torque down control is attained at such a timing, the rotational speed of the engine is increased and that of the turbine is also revved up since the accelerator pedal is depressed by the driver in the power-on down shift. Thus, disadvantageous shift characteristics such as an increase in the shift shock, a delay in the time for completing the shift, lack of responsiveness, an increase in a thermal load to frictional engagement elements and the like may appear.